Bilateral coordination and the motor basis of female preference for sexual signals in canary song

Abstract

The preference of female songbirds for particular traits in songs of courting males has received considerable attention, but the relationship of preferred traits to male quality is poorly understood. There is evidence that some aspects of birdsong are limited by physical or physiological constraints on vocal performance. Female domestic canaries (Serinus canaria) preferentially solicit copulation with males that sing special high repetition rate, wide-band, multi-note syllables, called `sexy' or A-syllables. Syllables are separated by minibreaths but each note is produced by pulsatile expiration, allowing high repetition rates and long duration phrases. The wide bandwidth is achieved by including two notes produced sequentially on opposite sides of a syrinx, in which the left and right sides are specialized for low or high frequencies, respectively. The temporal offset between notes prevents cheating by unilaterally singing a note on the left side with a low fundamental frequency and prominent higher harmonics. The syringeal and respiratory motor patterns by which sexy syllables are produced, support the hypothesis that these syllables provide a sensitive vocal-auditory indicator of a male's performance limit for the rapid, precisely coordinated inter-hemispheric switching, which is essential for many sensory and motor processes involving specialized contributions from each cerebral hemisphere.